A man developed left-sided proptosis and orbital edema that progressed during a three-week period. Ten years ago he had a skin lesion of the left lower lid excised and the histopathologic diagnosis then was granular cell myoblastoma. In 1972, the tumor recurred; a biopsy was again performed, but no definite diagnosis was made despite multiple consultations from general and ophthalmic pathologists. Biopsy specimens of the orbit, lids, and preauricular lymph node taken in 1974 showed a poorly differentiated mucus-secreting adenocarcinoma. A comparison of the three biopsy specimens showed cells with similar characteristics. Medical evaluation failed to reveal a primary tumor elsewhere in the body. The tumor most likely arose locally from an eccrine sweat gland. This is the second reported case of an adenocarcinoma of an eccrine sweat gland invading the orbit. The tumor, usually considered radioresistant, was successfully treated with radiotherapy, and the patient has remained free of tumor for 18 months.